Most of mine have been as healer, I've tanked once and got a commendation then, as dps I've actually gotten two while on my summoner, I think from the healer who acknowledged my response to tanks being dumb (yes hug the self destructing bomb) by using titan and keeping stuff off them. I do tend to give mine out to healers, but as a healer it's whoever was either nicest or kept me safe.

When I played swtor I'd go out of my way to thank dps after a run if they went the extra mile to keep me safe. So I hope there are other healers like that that will give the good dps the commendations they deserve.